We now analyze how BC is affected at the group level when a model is updated due to new data being acquired. We evaluate how per-group accuracy and NFR are affected when updated models are obtained by empirical risk minimization (ERM) or by worst group risk minimization (e.g., minimax group fairness [1]}, [2]} or group distributional robustness [3]}). Lastly, we propose a method to account for the worst NFR at group or at sample level, and show how this can improve the updated model in terms of group BC.
